Communication system



June 6, 1939.

H. J. NICHOLS ET AL COMMUNICATION SYSTEM MB/i Rf Filed Dec. 12, 19:55

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I Patented June 6, 1939 umreo STATES PATENT OFFICE 2,161,586 COMMUNIC A'IION srs'rnu" Harry J. Nichols, Binghamtom and Henry L. Tholstrup, Endwell, N. Y., assignors, by direct and mesne assignments, to International Business Machines Corporation, New York, N. Y., a corporation of New York v Application December 12, 1935, Serial N0. 54,134

' 11 Claims. (c1. rap-53.1)

This invention relates to a communication system and more particularly to such a system as a printing telegraph or the like system.

It is the principal object of the invention to provide a novel communication system forthe rapid, eflicient, and accurate transmission of intelligence.

It is a further object to provide a selective signalling system in which the number of required selection intervals is greatly reduced, providing for increased speed and accuracy in transmission.

It is a further object to provide a signalling system of this character in which a selection of 'a desired element is effected through the utiliz'ation of signals having predetermined time relationship and also having other distinguishing characteristics. I

It is a still further object to provide such a system in which the selectable elements are divided into a plurality of groups, each'group having a predetermined time relationship with respect to the others, and in which further selection of the desired element in any group is effected in ac cordance with predetermined distinguishing characteristics of the signals.

Other objects and advantages will be apparent from the description, the accompanying drawings, and the appended claims.

In printing telegraph systems, the single impulse signal system, as contrasted with coded signal systems,- depends in the matter of selection upon dividing a predetermined basic time period (usually the period of single revolution of a. rotating member which imparts the time characteristic to the signals) into fractional time intervals in which the individual selections are performed. Thetimed signals representing the predetermined selections are thus diflerentiated from eachother by the times at which they appear "with reference to the beginning of the basic time period. The beginning of the basic time period may be marked by a start or synchronizing signal, or it maybe unmarked, reliance being placed on the establishment, and maintenance of a synchronous relation between the sending and receiving machines.

In the novel system herein disclosed, thebeginning of the basic time period is preferably marked by. a preliminary .or start signal, and each fractional time interval may represent a plurality of desired selections, the particular selection depending on the character and timing of the start-and/or printing signals.

The start signal and printing signals may be characterized by polarity, frequency and/or amplitude. It is found, however, that the simplest and most reliable characteristic, other than that, I

of time, which can be imparted to a single signal impulse is that of polarity. Hence, in the following description, the added characteristic by which the group and sub-group selections are indicated will be referred to as polarity. It should be understood, however, that the signals may be given other selective characteristics if desired; for example, when carrier current transmission is used, the signals may be differentiated by time and frequency characteristics. Such a system is-disclosed in copending applica-' tion, Serial No. 7,674, filed February 23, 1935, and is adapted for use in conjunction with the present invention.

In the embodiment herein disclosed, the preliminary signal performs two functions, namely. to start a selecting device at the receiving machine, and to divide the selectable elements into two groups, each group comprising two subgroups. The selecting or printing signal likewise performs two functions, namely, to select one sub-group of the group previously selected by the preliminary signal in accordance with the time relationship of the printing signal with respect to the preliminary signal, and to select the predetermined selectable element from the sub-group in accordance with the characteristics of the printing signal. For the'sake of brevity, the preliminary signal will be referred to as the start signal, and the selecting signals as printing signals. This arrangement provides for reducing the number of required time intervals by arranging a number of selectable elements to be actuated at the same time interval, but in response to different characteristics of the signals. In the preferred practicing of the invention, start signals of two different characteristics are used,

that is, a positive and negative polarity. De-

pending-upon which start signal is sent, one or the other group of selectable elements is selected, the final selection of the predetermined element or group of, elements, being made by the printing signal in accordance with its time relationship with respect to the start signal. A still further ther divided into two sub-groups, the final selection being made in accordance with the characteristics of the start signal, and the character and timing of the printing signal.

Thus a plurality of selectable numbers are arranged in the same time. relationship (four in the embodiment of the invention herein described) and the desired selection is made in accordance with characteristic signals. This greatly reduces the number of time intervals required. The basic time period is thus divided into selection intervals equal in number to one fourth of the number of selections to be performed, plus one interval for the start signal. This reduction in the number of time intervals required is of very great advantage, and provides for greatly increasing the speed of transmission, improving the accuracyof transmission, increasing the number of selections performed by the system, or for obtaining a combination of several or all of these advantages in part.

In the drawings, Fig. 1 is a diagrammatic view illustrating the advantage of the system of the present invention as compared to a typical single impulse signalling system;

Fig. 2 is a view in schematic form showing an embodiment of the invention as applied to the transmitting end of a typical printing telegraph system;

' Fig. 3 is a similar view showing a modified arrangement of transmitting apparatus;

Fig. 4 is a view showing an embodiment of apparatus as applied to the receiving end of the system; and

Fig; 5 is a view in schematic form showing an apparatus adapted for both sending and receiving functions. I

In the several figures, excepting Fig. 1, like characters represent like parts.

Referring to Fig. 1 in detail, line A illustrates graphically the signals ofa typical single impulse printing telegraph system adapted to perform 32 selections and employing one periodic synchronizing signal (or start signal) and 32 timed printing signals, all signals being of equal length and character. The time period of one printing cycle, representing one revolution of cycle of the sending distributor, is the basic time period and is represented by the letter T. The speed of transmission of intelligence over the system is inversely proportional to the period T. In such a system, assuming that N selections plus a synchronizing or starting function are to be performed, the signal impulses are sent during a fractional time unit equal to T divided by N+1. This fractional unit, which may be termed the selection interval since each selection is made during one of such units,is designated in the figure by t, and theoretically represents the duration of a signal impulse. In practice, some synchronizing margin is required, and the signals are somewhat shorter than the selection interval. In the. figure, the signal impulse i' is shown as occupying two thirds of the selection interval t, the synchronizing margin m, one third of the selection interval.

Line B illustrates graphically the signals in accordance with the present invention. It is as sumed that the distributor speed is the same as in the previous instance, hence the basic time period is likewise represented by T. In this case, the printing signals are preceded by an equal start signal, and under the same assumptions as to the capacity of the system, the selection interval t is equal to T divided by the sum of N/4 plus one. This follows from the system of signalling of the the first interval.

invention which enables four selections to be accomplished during each selection interval except The relative lengths of the signal 2' and synchronizing margin m are the same as in previous case. Fig. 1 represents comparative conditions when the present invention is utilized to provide lengthening of the signal impulses without increasing the speed of transmission. In such case the accuracy is very much increased, by reason of the greater length of time that the rotary contactor remains in contact with each of the segments. As above explained, however, the invention provides for obtaining combined advantages of increased speed of signalling, together with a partial lengthening of the signal impulses and synchronizing margin toprovide increased speed, accuracy, and reliability of transmission. Thus if the signal lengths are maintained the same as in a typical single impulse system, the speed of transmission with comparable accuracy and reliability can be increased very materially, for example, in excess of three and one half times, with a system providing the number of selections indicated above. It also provides for obtaining a great increase in speed of transmission with comparable accuracy and reliability where such object is particularly desired.

Referring to Fig. 2 in detail, the apparatus shown performs the function of transmitting the nals, are collected from their respective circuits,

by two similar distributors Q, Q. Each rotary distributor includes a rotary contactor 20, 20 suitably driven, as for example by friction, by a drive shaft (not shown) at a predetermined speed. The brushes of the rotary contactors are normally held in a predetermined rest position on a particular segment 1', r' by pawls 24, 24' adapted to be actuated by release magnets 23, 23'. When released, rotary contactors 20, 20' sweep at uniform speed over the face of the stationary elements of the distributor comprising rings 2|, 2|, a double seriesof insulated segments, a, b, c, (1, etc., and an elongated segment 22, 22'. The segments associated with the signaling function, designated by a, b, c, d, etc., are arranged in pairs, segments a and b of distributor Q being shown as located in the same time interval, the first following the rest segment r,-so that they are simultaneously contacted by rotary contactor 20; similarly segments c and d of distributor Q are located in the first time interval following rest segment r and are arranged to be simultaneously contacted by rotary contactor 20'. The segments associated with each contactor are preferably mounted in three circles concentric with the ring and the axis of the rotary contactor. These parts are illustrated in linear development in order to simplify the diagram. The two distributors Q, Q may be positioned independently of each other, but preferably are placed concentrically in the same or in different planes to produce a more compact structure, a common drive means in such case serving to drive both contactors. The two distributors do not function simultaneously, but the signalling operations to be transmitted are divided between them and only that distributor and its rotary contactor associated with the operated key is released and placed in rotation.

Four printer actuating or sending keys Ka, Kb, Kc, Kd are shown, each key representing one of a sub-group. The two sub-groups represented by keys Ka, Kb are associated with distributor Q, the two sub-groups represented by keys Kc,

Kd with' distributor Q". Key Ka' represents the sub-group adapted to send a combination of start and printing signals of distinctive character, say a positive start signal and a positive printing signal, while key Kb represents the subgroup sending a positive start signal and a negative printing signal, the signals ineach instance being sent via distributor Q. In like manner, key Kc represents the sub-group sending a negative start signal and a positive printing signal, while Kd represents the sub-group sending a negative start signal and a negative printing si nal. the signals in each instance being sent viadistributor Q. The start signals sent by the,

group comprising the two sub-groups represented by keys Ka, Kb are positive; the start signals of the group comprising the two sub-groups represented by keys Kc, K'd are negative. The four keys named send printing signals during the same selection interval and hence the signals are not differentiated with respect to time. It will be understood that other similar groups and subgroups of keys are arranged to send similar signals at other time intervals. For example the following table illustrates a suitable arrangement providing for the sending of distinctive signals for 32 operations, making use of 8 time intervals. In the table, the Roman numerals indicate the time intervals within which the second or printing signal is transmitted with reference to the first or starting signal,

Start Printing I Start Printing signal signal signal signal +V I V +V I -V II VI +11 II -VI +111 +II +III II +III +VII -III -VII +IV +VIII IV VIII +lV +VIII --IV VIII 'Ps, Ns respectively. These bussesare connected to the terminals of a line connecting device, in this case a center tapped resistor 23 whose te rminals are also connected to line terminals 26,

21. The center tap 29 is connected to the frame.

Battery B, or other source of direct current, provides a current for signalling purposes. One

. side of battery B is connected to rings 2|, 2|,

- ate universal bail UB2 which in turn actuates the other side to the frame or ground which is thus established at negative potential.

The group of keys represented by Ka and Kb,

including all the keys associated with distributor Q, actuate a universal bail UBI which in turn actuates auxiliary switch XI Likewise, the group of keys represented by K0 and Kd, including all the keys associated with distributor Q, actuswitch X2. Auxiliary switch Xi closes the circuit from send bus Ps-via capacitor CI to release magnet 23. Capacitor Ci, normally uncharged, functions in cooperation with auxiliary switch XI to restrict release magnet 23 to one operation for each operating cycle of switch Xi, and thus prevents undesired repeat signals from being sent to the line in case the operator holds a key of the first group depressed overtime.

Auxiliary switch X2 and capacitor C2 perform the same functions with respect to keys of the second group.

Latch magnet 25, the function of which is to latch down the depressed key and at the same time to lock all other keys against depression until the sending cycle is completed, is connected on one side to the elongated segments 22, 22' and on the other to the junction between capacitor C3 and resistor R3. Capacitor C3 is nor mally maintained in charged condition through resistor R3.

The operation when sending is as follows:-

Assuming first that keyKa is depressed, the contacts of key switch Xa are closed, and simul-' taneously, through the agency ofuniversal bail UBI, the tongue member of auxiliary switch Xi is moved to the lower contact. The latter action' completes a circuit from positive battery to ring 2|, via rotary contactor 20' to segment a r, thence through the winding of release magnet 23, via contacts of switch Xi and capacitor Ci to send bus Ps, through resistor section 28a and center tap connection 29 to frame and return to negative battery. A local current pulse through this circuit energizes release magnet 23, causing pawl 24 to release rotary contactor 20 which is quickly set in motion by its drive means which operates continuously at substantially constant speed. It should be noted that center tapped resistor 28 is connected across line terminals 2G, 21. The receiving end of the line terminates in some suitable item of receiving equipment such as a relay, transformer, etc., which completes the line circuit, hence part of the current pulse flows from terminal 26 through current pulse, and hence the line signal caused thereby,:flows until capacitor Ci is fully charged, but capacitor Cl is made of such value that the current flow preferably is reduced to negligible value by the time contactor-2|| leaves rest segment 1'. The signal transmitted as just described constitutes the start signal and its direction in the line is-such as torepresent positive polarity.

When rotary contactor 20 reaches elongated segment 22, a second local circuit can be traced from ring 2| via contactor 2|! to segment 22, through the winding of latch magnet 25, via capacitor C3 to ring 2|. Capacitor C3, being already; charged, discharges through the circuit just traced, energiz ng latch magnet 25 whose latch member 25a hooks over the depressed key Ka and underneath all other keys, locking the keyboard in status duo, and preventing release ofthe operated key until the end of the transmitting cycle, and preventingoperation of any other key during this time. Latch'magnet 25 A through resistor R3. The arrangement described provides a strong operating pulse to magnet 25 followed by reduced holding current, economizing on current and facilitating the prompt operation of the latchand subsequent release of the keyboard when contactor20 leaves segment 22.

When rotary contactor reaches segment a. a third local circuit is established from ring 2| via. contactor 20 to segment a, via contacts of switch Xa (held closed by the locking of the keyboard) to send bus Ps, and thence returning to negative batteryby the path traced for the starting pulse. The current pulse. through this circuit, continuing for the duration of the contact between contactor 20 and segment a, sends a corresponding positive signal to the line. This signal constitutes the printing signal for character A (for example), and is characterized by its polarity and by its timing relative to the start signal. Near the end of the revolution of contactor 20, the circuit of latch magnet is broken as the contactor leaves segment 22, and latch member 25a is promptly withdrawn by the action of retractile spring 25s, unlocking the keyboard and permitting key Ka to rise under the action of its retractile spring (not shown). Universal bail UBI rises with key Ka due to the reaction of the spring tongue of switch XI. As the upper contacts of switch XI close, capacitor Cl is quickly discharged through resistor RI, restoring normal conditions in this circuit. At the end of the revolution, rotary contactor 20 is stopped on rest segment 1- by reason of being intercepted by pawl 24.

Assuming next that key Kb is depressed, the operations relating to the sending of the start signal, the release of rotary contactor 20, and the locking and unlocking of the keyboard are the same as described in connection with the operation of key Ka. Key switch Xb, operated upon the depression of key Kb, is connected to segment b andnegativesend bus Ns. Hence, when rotary contactor 20 reaches segment b, the local signalling pulse flows via send bus N8 and resistor section 28b to center tap 29; also in the line from terminal 21 through the line circuit to terminal 26, thence through resistor section 28a to center tap 29. Thus the current flow in the line circuit is in the opposite direction as compared with the previous case, and under the assumptions made, key Kb sends a printing signal of the same timing as that sent by key Ka, but of negative polarity.

Assume next that key Kc is depressed. In this instance, universal bail UB2 is actuated, closing the tongue member of auxiliary switch X2 to its lower contact, while at the same time the key closes the contacts of switch Xc. The local circuit first established is from positive battery to ring 2| via contactor 20 to segment 1', through winding of release magnet 23, via. contacts of switch X2 and capacitor C2 to negative send bus Ns, and resistor section 28b to center tap 29; also through the line circuit, resistor section 28a, center tap 29 and to ground, and to negative battery. The pulse through this circuit operates release magnet 23, charges capacitor C2, and sends a negative start signal to t"! line. Rotary contactor 20' is released by the operation of release magnet 23, and is set in motion by its drive Assuming next that key Kd is depressed, it will be seen that following the analysis of the sending of the start signal by key Kc and of the printing signal by key Kb, a negative start is sent via distributor Q, and a negative printing signal via segment (1 of distributor Q, all other operations being as described in connection with the previous cases.

The four examples given represent, as regards the signals sent to the line, two groups, the desired one of which is predetermined in accordance with the polarity or other distinguishing characteristic of the start signal, and four subgroups of signalling elements, two sub-groups associated with each main group, the final selection being determined in accordance with the polarity or other distinguishing characteristic of the printing signal.

The signals in the above exaniples are sent in nals being difierentiated by time with relation to the start signal, that is, the selection interval with which they are associated. Hence the signals sent by each individual key become distinguished by reason of their combined time and other distinguishing characteristics.

It will be apparent to those skilled in the art that various suitable arrangements may, following the teaching of the present invention, be used to cause the reversal of the polarity of the line signals or to impart other variants in their character, and all such variations should be, and are intended to be, encompassed in theterms of the appended claims.

It is not necessary that the transmitting apparatus embody a plurality of rotary distributors and Fig. 3 shows an embodiment of a signal transmitter in accordance with the invention in which only'one distributor is used, and in which four signalling keys are operatively associated with each transmitting segment. The four keys shown represent other similar groups of keys (one key for each selection to be performed over the system) making up a complete transmitting keyboard. Keys Ka, Kb, Kc, Kd are each provided with an individual key switch Xa, etc., but in this case four key switches'are connected in common on one side to segment I of distributor Q; and on the other side, alternately to positive send bus Ps and negative send bus Ns.

Auxiliary switches XI and X2 operatively assoelated with keys Ka, Kb, and Kc, Kd, respectively, connect in common to release magnet 23, but separately to send bus Ps and Ns respectively. The remainder of the arrangement is similar to that of Fig. 2, omitting distributor Q and associated parts.

The operation is as follows:-

Upon the depression of any key, release magne 23 is connected in a local circuit byeither switch XI or X2,'hence rotary contactor 20 is released, and a start signal of proper polarity is sent to the line. For keys Ka and Kb-and allmother keys associated with switch Xi, the start signal has positive polarity; for keys Kc and Kd and all other keys associated with switch X2 the start signal has negative polarity. When rotary contactor 20 reaches segment I a circuit is completed via the key switch associated with the depressed key to the proper sending bus to transmit a signal of proper polarity. Thus actuation of keys Km and Kc causes the sending of positive printing signals, and keys Kb and Kd the sending of negative printing signals, in the first time interval following the start signal. Other groups of keys function similarly in other time intervals. The operations of locking and unlocking the keyboard, etc., are as described in connection with Fig. 2. Without further detailed analysis, it will be clear that the operation of the system andghe sending of proper characteristic start and printing signals are the same as described above in connection with Fig. 2.

Referring now to Fig. 4 in detail, keys K0, Kb, etc., of the receiving apparatus correspond to those similarly designated at the sending apparatus in Fig. 2, but function at the receiving station to actuatethe printer mechanism to print the selected character and to perform other functions relating to printing such as spacing, carriage return, shifting, etc. Keys Ka, Kb, etc., are

actuated by key magnets Ma, Mb, etc., which constitute the selectable elements of the receiver.

Key magnets Ma, Mb, etc., are connected to seg- 5 merits a, b, etc., on one side and to receive busses PnNr according to group. It will be understood that the key magnets for the group of keys correspending to those sending positive printing signals are connected to positive receive bus P1: and

those for the group associated with negative print ing signals are connected to negative receive bus N'r. The two distributors Q, Q, with associated release magnets 23, 23' are similar tothose of similar designation in. Fig. 2, except that elongated segments 22, 22' are omitted since they have 36 no relation to the receiving function. The distributors are arranged to be suitably driven by means similar to that at the transmitting apparatus, such as the friction drive means, providing for the driving of the distributor when released at 40 a speed corresponding'to that of the distributor at the transmitter.

A suitable coupling device, such as transformer 30, connects the line to the receiving instrument,

which in this instance comprises two electronic 48 relays TI and T2. Each electronic relay is preferably of the grid-controlled, gaseous discharge type and provided with a control grid, a plate or anode, and cathode, all contained in a sealed envelope containing gas or vapor following the 50 well known construction of these devices.' The two electronic relays. are arranged, in push-pull. fashion on the input side, the. signals from theiine being applied to the grids of relays Tl, T2 by input transformer 30 provided with primary SOp'and 5 center-tapped secondary 30s. The current for the anode circuits of TI and T2 is supplied by battery B I and the grids are given a normal nonoperating bias .by battery B2 connected between the cathodes and the center tap of secondary 30s.

The arrangement is such that line signals make one grid more positive, andthe other more negative, in accordance with the polarity of thesignals.

As is well known, the grid of agaseous discharge tube can start the ionization of the tube but is 5 normally unable to stop the discharge through the tube when once started; Acut-ofl relay 32, of

retarded action type, is therefore provided to cut off the current in the anode-cathode circuits of the electronic tubes after a predetermined time interval. .The cut-off relay is timed to operate less quickly than the other magnets in circuit with it, and to hold the circuit open long enough to cause deionization of the tubes, thus permitting 75 the grids to regain control. It will be understood by those skilled in the art that a polar relay with tongue set to neutral positionycan be used instead of the electronic relay arrangement shown which is equivalent in its action to that of a neutral polar relay. The electronic relay arrangement shown 5 has practical advantages, however, in that it operates only when a definite signal value obtains, is virtually instantaneous in action, and does not require the critical adjustments which characterize the polar relay. 10

The operation of the receiving equipment is as follows:

Assume that a positive start signal followed by -st-'pt'ositive printing signal has been sent from the sending machine by the depression of key Ka. 5 When the positive start signal is received from the line, transformer 30 makes the grid of one tube, say tube Tl, more positive than normal,

' while the grid of the tube T2 is made correspondingly more negative than usual. Assuming that go the signal is of prorer amplitude, tube TI is ionized while tube T2 is momentarily guarded against ionization. Tube Ti becomes conducting upon ionization, and a local current pulse flows from positive Bl, through the winding and contacts of 5 relay 32 to ring 2|, via contactor 20 to segment 1'', through the winding of release magnet 23 to positive receive bus Pr, thence to the plate of tube Ti, via the ionized electron stream to cathode and return to negative Bi 30 y In response to this current pulse, release magnet 23 releases contactor 2B which is quickly set in motion by its drive means, and shortly there-- after, cut-off relay 32 opens its contacts, termina in the current pulse and causing tube TI 5 to deionize, thus permitting its grid to regain control. Relay 32 immediately closes its contacts, re-

storing normal circuit conditions. As contactor 20 reaches segments a, b, the positive printing signal is received and tube Tl again ionized. This on time the pulse circuit is established via segment a through the winding of magnet Ma to positive receive bus Pr and thence through tube -TI .to negative Bl. The pulse throughthis circuit energizes magnet Ma, actuating its associated printer 45 key and causing the selected character to be printed. As in the previous instance, the pulse is terminated by the opening of the contacts of cut-off relay 32 and tube TI is deionized, restoring normal circuit conditions. Assuming next that key so Kb at the transmitter has been depressed, the signals sent to the line comprise a positive start sigtactor 20 reaches segments a, b, the negative printing signal is received and tube T2 ionized, in effect connecting receive bus Nr to battery Bi.

Hence magnet Mb is energized, actuating its as- 60 sociated printer key and causing the selected character to be printed;

As an example of the third case, assume that a key Kc at the sender has been'depressed, sending a negative start signal'followed by a positive printing signal of the same timing as in the previous case. Tube T2 is ionized by the start signal, in effect connecting receive bus Nr in circult, and causes rotary contactor 20 to be released. As'rotary contactor 20' reaches segments 0, d, the positive signal arrives to ionize tube Tl.

Receive bus P1 is thusconnected in circuit, and

magnet Mc energized causing the selected character tobe printed.

As an example of the fourth case, it is assumed I that key Kd at the sender has been depressed, sending a negative start signal and negative printing signal to the line. Tube T2 is thus ionized twice in succession, the first time causing rotary contactor 20' to be released, and the second time causing magnet Md to be energized, thus eifecting the printing of the selected character.

Without further analysis, it will be clear that by following the teaching of the invention other sub-groups of sending elements which send signals of the same timing can be utilized to control corresponding sub-groups of selectable elements in the same manner as the sub-group of sending keys K0, Kb, Kc, Kd and of control magnets Ma, Mb, Mc, Md.

Referring now to Fig. 5 in detail, the arrangements of Figs. 2 and 4 aretherein shown combined into a send-receive arrangement capable of alternately sending or receiving messages merely by operating a switch to make suitable changes in the circuit connections.

, Keys Ka, Kb, Kc, Kd, which constitute the printer actuating keys, are each provided with an individual key switch Xa, etc., and an individual actua ng magnet Ma, etc. The key switches are of break-make type, the tongue and upper contact normally connecting the associated key magnet to the associated segment of the group distributor. The tongue and lower contacts, when closed, connect the associated segment to the proper send bus, Suitable switching arrangements are shown to establish the proper circuits for sending andreceiving conditions, the switch elements being shown at convenient locations in ,the diagram, but in practice are ganged into a single switch having Send, Receive and Neutral positions. The remaining parts are the same as shown in Figs. 2 and 4.

Considering first the sending operation, it is to be understood that all switches have been closed to the position indicated by S. Upon the depression of key Ka, the tongue of key switch Xa is moved to the lower contact and universal bail UBI closes the tongue of auxiliary switch XI to the lower contact. Rotary contactor 20 is thereupon released, latch magnet 25operated, and positive start and printing signals transmitted as described in connection with Fig. 2. The sending operations upon the depression of keys Kb, Kc, Kd are likewise as described in connection with Fig. 2. Additional sub-groups of keys, following the pattern of the sub-group including key K0, etc., can be added to the system to the extent desired, in other time interval positions.

Considering next the receiving operations, for receiving the gang switches are moved to position R disconnecting auxiliary switches XI, X2, latch magnet 25, and resistor 28 together with the sending busses, and connecting transformer 30 to the line. The receiving-operations as described in connection with Fig. 4 then become applicable to Fig. 5.

It will thus be apparent that the embodiment of the invention just described provides an efll cient send-receive arrangement in which the larger part of the apparatus functions both in sending and receiving, with consequent advantages in respect to simplicity and low costs.

The invention herein described enables any number of selections to be accomplished over a single circuit by a combination of two signals of equal magnitude, the first signal being invariable with respect to time, but determinately variable in character, while the second s gnal is determinately variable with respect to time and character. Other combinations of characteristicstart and printing signals may be made as desired to provide the same, less, or even a greater number of selection steps in any one time interval, the invention thus providing a system of signalling which provides for obtaining great speed, accuracy and reliability.

While the methods described herein, and the forms of apparatus for carrying these" methods into effect, constitute preferred embodiments of the invention, it is to be understood that the in vention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a communication system of the character described the method of signalling which comprises the steps of sending a preliminary signal of distinctive character indicative of a selecting starting operation to be performed, and thereafter sending a second signal having predetermined time relation to said preliminary signal, said signals being indicative of a desired operation to be performed; receiving said signals, utilizing said first mentioned signal to select from a plurality of rotary elements the one element predetermined in accordance with the characteristics of said preliminary signal, releasing said selected rotary element from a predetermined phase position, and utilizing said second mentioned signal in cooperation with said selected rotary element to sired.

2. In a communication system of the character described, the method of signalling which comprises the steps of sending a start signal of distinctive character indicative of a selective starting operation to be performed, and thereafter sending another signal in predetermined time relationship with said start signal, said signals being indicative of a specific operation to be performed; receiving said signals, effecting a predetermined group selection as determined by the characteristics of said start signal, and effecting a further selection from the selected group and performing the operation desired as determined by the time relationship of said second signal with said start signal.

3. In a communication system of the character described the method of signalling which comprises the steps of sending a start signal of distinctive character, sending a second predetermined timed signal having predetermined characteristics with respect to said start signal, said signals being indicative of a desired operation to be performed; receiving said signals, effecting a predetermined group selection as determined by the characteristics of said start signal, and effecting a further selection from the selected group and performing the desired operation in accordance with the characteristics of said second signal and the time relationship thereof with respect to the start signal.

4. In a communication system of the character described the method of signalling which includes the steps of sending a start signal of predetermined polarity characteristics indicative of perform the operation as de- ,a selective starting operation to be performed,

and thereafter sending a second signal having predetermined characteristics with respect to said start signal, said signals being indicative of a desired operation to be performed; receiving said signals, effecting a predetermined group selection as determined by the polarity characteristics of said start signal, and effecting a further selection from the selected group and performing the desired operation in accordance with the characteristics of said second signal.

5. In a communication system of the character described the method of signalling which includes the steps of sending a start signal of distinctive character, sending a second signal in predetermined time relationship with said start signal aflhe start signal and said second signal, and in accordance with the distinctive characteristics of said second signal.

6. In a communication system of the character described, the method of signalling which includes the steps of sending a start signal of distinctive character, sending a second signal in predetermined timed relationship with said start signal and of predetermined polarity characteristics, said signals being'indicative of a desired operation to be performed; receiving said signals, effecting a predetermined group selection as determined by the characteristics of said start signal, effecting the further selection from the selected group and performing the desired operation in accordance with the time relationship between said start signal and'said second signal, and in accordance with the polarity characteristics of said second signal.

'7. In a communication system of the character described, the method of signalling which includes the steps of sending a start signal of distinctive polarity characteristics indicative of a selective starting operation to be performed, and

thereafter send-ing another signal in predeter-.

mined time relationship with said start signal and of predetermined polarity characteristics, said signals being indicative of a desired operation to be performed; receiving said signals, ef-. fecting a, predetermined group selection as determined by thepolarity characteristics of said start signal, and effecting a further selection from the selected group and performing the desired operation in accordance with the time relationship between said start signal and said second signal, and inaccordance with the polarity characteristics or said second signal.

8. In a communication systemof the character described, the combination of a keyboard, mean's operative upon the actuation of each of said keys for generating a start signal of distinctive characteristics, and including means for generating a second signal having predetermined timed characteristics with res ect to said start signal, said signals being distinctive for each of the operating keys, means for transmitting said signals, means for receiving said signals, a receiving keyboard having operating elements corresponding to those at the transmitter, and means for effecting the operation at the receiver of the element corresponding to that operated at the transmitter including means for selecting a predetermined group of said elements in accordance with the characteristics of said startsignal, and means for selecting the desired operating element from said group in accordance with the time characteristics of said second signal in relation to said start signal. I

9. In a communicating system of the character described, the combination-of a keyboard,

means operative upon the actuation of each of said keys for generating a start signal of distinctive characteristics, and for generating a second signalhaving predetermined characteristics with respect to said start signal, said signals being distinctive for each of the operating keys, means for transmitting said signals, means for receiving said signals, areceiving keyboard having operating elements c'orresponding'to those at the transmitter, and group selecting means for selecting the operating elemeht at the receiving station corresponding to that at the transmitting stationcomprising a plurality or rotary elements, means for selecting and ieleasing for operation a predetermined rotary element'including means controlled in accordance with the characteristics of said start signal, and additional means associated with the selected rotary element and controlled in accordance with the relationship between said second signal and said first signal for efiecting the final selection of the desired element.

10. In a. printing telegraph system of the character described, means for generating polarized start signals and timed and polarized printing signals, transmission means, means for receiving a said signals, individual selectable printer actuating means, group selecting means actuated by said start signals for selecting a predetermined group of said printer actuating means including means controlled in accordance with the polarity of said start signals, and means controlled in accordance with the timing and polarity of said printing signals for selecting the desired one of said printer actuating means.

11.- In a printing telegraph system of the character described, the method of signalling which comprises the steps of sending signals-indicative with respect to time of the beginning of a predetermined time interval and with respect to character of a selective operation to be performed, and thereafter sending, signals difierentiated as to time within said time interval and differentiated as to character, and then in accordance with said signal combinations effecting predetermined selective operations.

12. In a printing telegraph system, means for transmitting signal impulses indicative with respect to time of the beginning of a cyclic interval and with respect to character of a selective operation to be performed, and means for thereafter transmitting signal impulses differentiated with respect to time and character indicative of predetermined operations to be performed.

13. Ina printing telegraph system of the character described, a plurality of actuable elements, means for transmitting a characteristic signal combination upon the actuation, of any of said elements comprising means for transmitting a single impulse, indicative with respect \,to time of thebeginning of a predetermined cyclic interval, and with respect to characteristics of a group selective operation to be performed, and means for thereafter sending a single impulse having predetermined timed relation with respect to said first mentioned impulse.

14. In a printing telegraph system, in combination, means for transmitting in cyclic order a characteristic starting impulse followed by a printing impulse having predetermined characteristics in relation to said starting impulse,

means for receiving said impulses, a plurality of rotary distributors, a plurality oi! selectively operable elements, means controlled in accordance with the characteristics 01 said starting impulse for placing a predetermined one of said rotary distributors in operation, and means co-operating with said selected rotary distributor and operable in accordance with the characteristics of said printing impulse in relation to said starting impulse for selecting and effecting operation of the desired one of said operable elements.

15. In a communication system of the character described, the combination of a plurality of operative elements adapted to be selectively operated, means for sending signals indicative of the particular operated element comprising means for sending 'a start signal, and thereafter a second signal, including means for imparting to said start signal distinctive characterictics which are indicative of a group of elements including said operated element, and means to impart to said second signal a predetermined time relationship with said start signal indicativeof said operated element within the selected group.

16. In a communication system of the character described, the combination of a plurality of operative elements adapted to be selectively operated, means for'sending a distinctive signal 'combination'upon the operation of any of said elements including a preliminary. signal having predetermined distinctive characteristics, and a second signal having predetermined time relationship with said preliminary signal, a receiving station, means for receiving said signals, a plurality of operative elements at said receiving station, and means for operating the element at said receiving station corresponding to said operated element at the sending station including a plurality of rotary elements, means conwith the time relation between said second Sig-- nal and said preliminary signal.

17. A communication system of the'character described'comprising a plurality of operative elements adapted to be selectively actuated, a rotary member, means for retaining said member in a predetermined position of rest, means efiective upon the actuationof one of said operative elements for releasing said retaining means and placing said rotary member in-movement, means acting upon the actuation of any 01' said operative elements for sending a signal combination of distinctive characteristics for each such element, including means associated with the actuated element for sending a preliminary signal of distinctive charactristics indicative of a preliminary selective operation and for releasing said retaining means to place said rotary member in movement, and means also associated with said actuated element and with said rotary element for sending a subsequent signal of distinctive characteristics in predetermined time relation with said preliminary signal.

HARRY J; NICHOLS. I HENRY L. THOLS'IRUP. 

